Studies will continue on the mechanism of passive immunity of the gastrointestinal tract against viral infections, using transmissible gastroenteritis (TGE) virus in swine as a model. Different types of TGE viral preparations will be administered by different routes to pregnant swine, so as to determine the most appropriate procedure for (1) stimulating the production in milk of antibodies of the IgA class and (2) providing passive immunity of suckling pigs against intestinal infection with TGE virus. Attenuated and virulent TGE viruses will be studied in young pigs so as to characterize their differences in respect to: (1) infection of epithelial cells in various segments of the GI tract, (2) occurrence of villous atrophy, and (3) ability to stimulate active immunity. The occurrence and some of the characteristics of cell-mediated immunity against TGE viral infection in swine will be made.